Monitoring & metering
informed by the identification of hazards or suspected hazards, the potential exposure pathways, and the performance of equipment providing a barrier to these hazards. An important goal of monitoring during initial site entry is to establish safety zones at the site. Periodic monitoring is then conducted to ensure that any new hazards are identified promptly, and that appropriate controls are implemented to protect the responders and nearby communities.
WHY USE ION SCIENCE PIDS? Portable PID instruments such as the ION Science Tiger XT have been designed specifically for challenging field conditions. These rugged instruments benefit from the advanced features of the MiniPID 2 sensors, such as detection limits down to 1ppb, and measurement ranges up to 20,000ppm. Crucially however, the Tiger XT range is unaffected by the problems that plague other PID instruments. This is because a unique design eliminates any potential effects of varying humidity and contamination, and a built-in ASIC chip constantly checks PID performance to deliver a fail-safe instrument, which is essential in potentially hazardous applications.
In addition to the health risks posed by
VOCs, their accumulation in contaminated land can represent an explosion risk, so the ION Science portable PIDS benefit from global Intrinsic Safety (IS) certification for use in potentially explosive atmospheres. The Tiger XT is supplied as standard with a 10.6 eV lamp for the measurement of a wide range of VOCs. However, benzene is a particularly toxic VOC, and some site conditions set specific targets for this compound. Importantly, the new Tiger XT Select (XTS) utilises the ION Science 10.0 eV lamp to detect Total Aromatic Compounds
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(TACs) such as benzene, toluene and xylene, and is supplied with a pack of pre-filter tubes for the specific, selective detection of benzene. This speciation capability for benzene is a major advantage, given the complexity and cost of alternative benzene-specific measurement techniques.
ELIMINATING HUMIDITY INTERFERENCE For decades, the users of portable PID instruments have endured unreliable measurements from their instruments due to the high levels of humidity that often exist on- site and in the headspace of soil samples. This has been the source of enormous frustration, but the wide-ranging response and the sensitivity of PIDs has made them an important tool in site investigation and sample screening work.
A number of ‘work around solutions’ have been developed involving humidity suppression or compensation, but all of these have significant limitations:
Humidity sensor – these typically have a slower response than the PID sensor itself which causes a drifting compensation
Desiccant tube – these both slow and reduce the PID response, plus they need replacing from time to time which adds cost
Humidify the calibration gas – this only works at one level of humidity and is no longer accurate when the humidity changes
Importantly, none of these ‘solutions’ solves false positive readings at high humidity levels. ION Science has therefore developed a patent protected solution to high humidity, involving the addition of a third fence electrode within the
PID sensor. This overcomes the possibility of incorrect high readings by acting as a conductive break, and thereby preventing excessive current flow caused by the presence of high, and even condensing, levels of humidity.
SUMMARY In the many locations with hydrocarbon contamination, portable PIDs offer environmental consultants, engineering contractors, regulators and remediation companies the opportunity to quickly assess large numbers of samples and locations. These measurements are not used to demonstrate compliance with licence conditions, but they are essential for operational purposes; enabling rapid, low-cost risk assessments and enabling effective, informed, decision making during the remediation process. In the Tiger XT, users have a device that is truly fit for purpose; rugged, portable and sensitive to an enormous range of VOCs, but also resistant to the contamination and humidity issues that affect other manufacturers.
ION Science
www.ionscience.com
April 2023 Instrumentation Monthly
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